Epoxy resin, epoxy resin composition, epoxy resin cured product and composite material

An epoxy resin, comprising an epoxy compound having a mesogenic structure, and having a value η′2/η′1 equal to 3 or less, wherein η′1 is an initial dynamic shear viscosity in Pa·s and η′2 is a maximum value of dynamic shear viscosity in Pa·s, in a measurement of dynamic shear viscosity,

• wherein the initial dynamic shear viscosity η′1 and the maximum value of dynamic shear viscosity η′2 are measured with a rheometer, with a gap between a parallel plate and a stage of the rheometer of 0.05 mm, a frequency of 0.5 Hz, a strain of 8000%, and a constant temperature of 80° C., over 80 minutes in a continuous manner, and
• wherein the epoxy compound is represented by the following Formula (1):
• wherein, in Formula (1), each of R1, R2 and R3 independently represents a monovalent group, at least one of the monovalent groups represented by R1, R2 and R3 includes a mesogenic structure, and at least one of the monovalent groups represented by R1, R2 and R3 has an epoxy group.